German Transport Minister Alexander Dobrindt, who visited the scene, said it was a "horrifying sight".

"The drivers' cabs of both trains are wedged into each other. One side of one train is completely torn open. The other train bored into it," he told a news conference.

Bavarian Interior Minister Joachim Herrmann told the same conference it was "difficult to comprehend" how such a crash could happen given the amount of investment in railway safety following previous train accidents.

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Media captionGermany train crash: Aerials show crash site devastation

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Media captionRace to rescue train crash injured

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Both trains were partially derailed by the head-on crash

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Both trains were partially derailed in the crash

Electrical engineer Joe Adediran, who was on the train between Rosenheim and Holzkirchen, said that he had had a "lucky escape".

"At the first station, this train normally has to wait for five minutes or so for the opposite one to arrive. After a while, we started to move on to the next station without waiting for the opposite train," he told the BBC.

Other fatal German train crashes

January 2011: 10 killed in Saxony-Anhalt when commuter train collides with goods train after driver runs through two signals

February 2000: Nine dead when overnight train from Amsterdam to Basel crashes near Cologne

June 1998: 101 killed when a high-speed train with a broken wheel derails and smashes into a bridge at Eschede in Lower Saxony

The scene of the crash is close to the Mangfall river in a hilly and densely wooded region.

The Munich blood bank issued an appeal for blood donors on its Facebook page (in German).

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Some passengers were still trapped in the wreckage hours after the crash